<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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  <body></body>
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<script>
  var apple1 = "青苹果";
  var apple2 = "红苹果";
  var nullBox = null;
  nullBox = apple1;
  apple1 = apple2;
  apple2 = nullBox;
  console.log("apple1青苹果变成了:" + apple1);
  console.log("apple2红苹果变成了:" + apple2);
</script>
